I need to weight how much activity has been in a Wordpress blog. Say, some day there are 3 posts and 10 comments, the points awarded for a post is 10 and just 1 for a comment, then said day had 40 points in total. However, there might be some days with no post activity or with no comment activity.

My first idea was a simple LEFT JOIN from the posts to the comments table. However, this will exclude days without posts. I'm no MySQL guru, but I've been researching and it seems that the best way to solve this is a with FULL OUTER JOIN (explained by Jeff Atwood), but MySQL doesn't suppor this!

Then, there actually is a workaround, but it's not working for me. It seems that the RIGHT OUTER JOIN is not returning what I need.
Here's the LEFT one, it works pretty good.

SELECT
DISTINCT DATE(post_date) AS day,
COUNT(ID) AS post_total,
COUNT(comment_ID) as comment_total,
(COUNT(ID)*10 + COUNT(comment_ID)*1) AS total
FROM wp_posts
LEFT OUTER JOIN wp_comments ON
DATE(post_date) = DATE(comment_date)
GROUP BY day ORDER BY total DESC

But something's wrong with the RIGHT one.

SELECT
DISTINCT DATE(post_date) AS day,
COUNT(ID) AS post_total,
COUNT(comment_ID) as comment_total,
(COUNT(ID)*10 + COUNT(comment_ID)*1) AS total
FROM wp_posts
RIGHT OUTER JOIN wp_comments ON
DATE(post_date) = DATE(comment_date)
GROUP BY day ORDER BY total DESC